Scale Surface and Scale/Alloy Interface for Alumina-Forming Alloys with Noble Metal and Yttrium

Scale surface and scale/alloy interface for alumina-forming (Fe-20Cr-4Al) alloys with noble metal (palladium, platinum) and yttrium were studied in oxidizing atmospheres (oxygen, oxygen-water vapor) for 18ks at 1473, 1573 and 1673K, by mass gain measurements, amount of spalled oxide, X-ray diffraction (XRD), scanning electron microscopy (SEM) and field emission-transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS). After oxidation at 1473K for 18ks in oxygen, the mass gains of the FeCrAl, FeCrAlPd and FeCrAlPt alloys showed almost the same values. Those of the FeCrAlY alloys decreased with increasing yttrium of up to 0.1% followed by an increase with the yttrium content. The mass gain of the FeCrAlPtY alloys with appropriate additions of platinum and yttrium were lower than that of the FeCrAlY alloy with 0.1mass% yttrium, and alumina/alloy interface of the alloy showed good coherency by TEM. The scale surface of the FeCrAl, FeCrAlPd and FeCrAlPt alloys were rough, however, those of the FeCrAlY and FeCrAlPtY alloys were smooth. After oxidation at 1673K for 18ks in water-vapor (47vol%), FeCrAlPt alloy with 0.5mass% platinum showed good oxide adherence. Platinum concentration was observed at alloy side of the alumina/alloy interface by FE TEM/EDS.

The Relationship Between Oxide Adherence and Porcelain-Metal Bonding

The lack of a reliable bond test has hindered the elucidation of the mechanism for porcelain-metal bonding in dental systems, because a test capable of detecting differences among porcelain-metal bonds of various qualities is required before the reasons for these differences may be ascertained. A method was developed in the present study whereby specimens of alloys with differing physical properties may be deformed to a constant strain to yield a fracture surface suitable for measurement of the area fraction of retained porcelain by an x-ray spectrometric technique described previously. The method proved sufficiently discriminating that significant differences could be found in 48 of the possible 66 comparisons among alloys and treatments. Linear regression analysis revealed a strong correlation (r 2 = 0.947) between the area fractions of retained porcelain measured in the present study and the oxide adherence strength values measured previously. This strong correlation, when considered in light of the literature evidence for the presence of an oxide layer at the porcelain-metal interface, provides compelling support for the oxide layer theory of porcelain-metal bonding in dental alloy systems.